1. Technical Field
The invention relates to a record carrier of a read-only type comprising information in a track.
The invention further relates to a method of manufacturing a record carrier of a read-only type in which method an information layer of the record carrier is provided with marks constituting a track representing information.
The invention further relates to a read device for reading the record carrier.
2. Related Art
Record carriers of a read-only type are well-known, e.g. the Compact Disc (CD). Such read-only type record carriers are manufactured in a mass production process, e.g. for optical record carriers by stamping replicas from a master disc. Hence the information is applied to the record carrier in one step, and the track has a single, continuing pattern of marks representing said information. The information is logically subdivided in addressable blocks of data words and corresponding control words, e.g. addresses. An addressable block is the amount of data words which is logically handled as one item of data, e.g. 2048 bytes. Hence the addressable blocks constitute logical amounts of user data which can be retrieved individually, e.g. computer data on a CD-ROM. On the other hand recordable-type record carriers are known, e.g. CD-R or CD-RW. Recordable-type record carriers are usually provided with information in a recording device by writing information signals in a preformed track consecutively or random at selected locations. Such recording in different sessions in time may take place in one recording device or in different recorders. The recording in different sessions of information signals adjacently in the track is called linking. A method and apparatus for linking successively recorded information signals on a recordable record carrier is known from U.S. Pat. No. 5,187,699. The minimal amount of information which has to be recorded without interruption by such an information signal is inter alia determined by the error correction system. Such amount is called an information unit and comprises a number of the logically addressable blocks, at least one but usually 8 or 16, and Error Correcting Codes (ECC) covering said blocks. Information units are to be recorded at predefined locations indicated by position information in the pregroove. Hence in between information units there may be a boundary between signals recorded at different instants, called a link position. In the known linking method, after a first information signal is completely recorded, the recording process is continued for a predetermined period after a last frame of the signal up to the link position. When a next information signal is to be recorded, the recording process is started at the link position by adding dummy information (usually zero data) up to the start of the following predefined location. Hence the area between the information units does not contain valid information, and is called a linking area, which linking area includes said link position. Usually the rules for the storage of information in the track on a record carrier are called a format, e.g. a format for recordable type record carriers. A problem is, that read devices for reading several record carrier types must first distinguish between the read-only type and the recordable type before the read signal can be decoded according to the correct format. Simple read devices which are equipped only to read the format of the record carriers of the read-only type may be disturbed when such a linking area is read, which results in errors in the output signals.
It is an object of the invention to provide a record carrier and read device which allow effective linking and obviate the above problems.
For this purpose, the read-only type record carrier as described in the opening paragraph has a track comprising the information subdivided in information units that are constituted by a predetermined number of addressable blocks, which track further comprises linking areas provided between the information units according to a format for recordable type record carriers. Further the device as described in the opening paragraph is provided with signal processing means for retrieving the information and discarding the linking area. The effect of the linking area in the read-only type record carrier is, that read devices need only be equipped for reading one format and can read the recordable discs without any disruption of the read process, because the linking area is part of the format. Further the compatibility between different types of record carriers is improved because the storage capacity of the read-only type record carrier is not larger than the capacity of the recordable type due to the presence of linking areas in both types, and because the relation between logical addresses of blocks and their physical locations can be the same in both types.
The invention is also based on the following recognition. Usually a lot of effort is required to provide linking for recordable type record carriers which are to be compatible to read-only type record carriers. Such a linking system may require a highly accurate recording device to create only a small linking area which can be dealt with by the error correcting system provided in players for read-only record carriers. By providing the linking area already in the read-only type disc format the read device is less complicated because only one format needs to be decoded. Further the recording device does not require a high accuracy linking circuit, but may create a normal size linking area.
A preferred embodiment of the record carrier is characterized in that the information is encoded by a channel code to an encoded signal comprising frames and in that the linking area comprises two frames. This has the advantage, that the first frame of the linking area may be used in a recording system to facilitate a run-out area for the previous information unit, while the second frame facilitates a run-in area for the next information unit. Hence a minimal loss of capacity is accomplished.
In a further embodiment of the record carrier at least one linking area comprises auxiliary information. This has the advantage, that the auxiliary information is exclusively available for read-only record carriers, for example copy protection keys, and cannot be easily copied to a recordable type record carrier, because on standard recording devices the contents of the linking area cannot be influenced externally.
Further advantageous, preferred embodiments according to the invention are given in the further dependent claims.